Electric discharge machine and machining method therefor

ABSTRACT

An electric discharge machine and method for carrying out electric discharge machining there within is provided, wherein after an electrode ( 21 ) and an electrode guide holder ( 25 ) are attached to an electrode holder ( 23 ), in advance, which is in turn mounted on a spindle ( 13 ), the electrode guide holder ( 25 ) is gripped by a gripper arm ( 29 ) and moved to a distal end of the electrode ( 21 ) so that the machining is carried out while the distal end of the electrode ( 21 ) is supported by an electrode guide ( 61 ). When the electrode ( 21 ) must be replaced due to the exhaustion thereof during the electric discharge machining of a fine hole, the electric discharge machine and method make it possible to assuredly carry out the replacement of the electrode in a short time.

TECHNICAL FIELD

The present invention relates to an electric discharge machine, to anelectric discharge machining method and, particularly to an electricdischarge machine and an electric discharge machining method suitablefor a case in which a thin rod-like or pipe-like electrode is used formachining a fine hole in a workpiece.

BACKGROUND ART

When a fine hole is formed in a workpiece by electric dischargemachining, a rod-like or pipe-like electrode is used to apply a voltagebetween the electrode and the workpiece so that the workpiece ismachined by electric discharge generated between them. As the electrodeis liable to be easily exhausted when used for machining the fine hole,the used rod-like or pipe-like electrode is generally long. The thin andlong electrode is liable to vibrate or flex during the electricdischarge machining, which might reduce the machining accuracy. Anelectric discharge machine in which an electrode guiding device forsupporting and guiding the electrode is employed to prevent thevibration or flexion from occurring is disclosed in Japanese Patent No.2,952,339. In the technology described in this Japanese Patent No.2,952,339, a fine hole machining electrode is used, and an electrodeguiding device for supporting and guiding the fine hole machiningelectrode and an electrode-induction device for inserting the electrodeinto the electrode guiding device are provided. The electrode isinserted into a guide hole of the electrode guiding device while beingnipped by the electrode-induction device, and a fine hole is formed byelectric discharge machining while guiding the electrode by theelectrode guiding device. Further, a method and an apparatus aredisclosed in the U.S. Pat. No. 6,396,022, in which an electrode magazineincluding an electrode guide having a pipe electrode inserted therein isreplaced in a spindle.

The prior art described in the above-mentioned Japanese Patent No.2,952,339 is problematic in that the electrode-induction device isrequired for inserting the electrode mounted on the spindle into theelectrode guiding device and in that a process for inserting theelectrode into an inner hole of the electrode guide is troublesome andtime-consuming because the thin and long electrode is liable to vibrateand/or flex. Also, the prior disclosed in the U.S. Pat. No. 6,396,022 isa system in which a plurality of large electrode magazines, eachincluding a pipe-like electrode, a collet chuck for holding and guidingthe pipe-like electrode and means for moving a vibration preventingguide and an electrode guide, are accommodated in advance in a magazinerack so that the electrode magazine is replaceable in the spindle, whichis problematic in that a structure thereof is complicated.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems in the prior art. An object of the present invention is toprovide an electric discharge machine and an electric dischargemachining method, which can eliminate a complicated process of insertingan electrode into an inner hole of an electrode guide every time whenthe electrode is exhausted due to the electric discharge machining andreplaced with new one, whereby the replacement of the electrode and/orthe electrode holder can be easily and assuredly carried out in a shorttime, and electric discharge machining including multiple processes cancontinue for a long period in an unattended operation, resulting in animproved efficiency of the electric discharge machining.

To achieve the above-mentioned object, according to a first aspect ofthe present invention, there is provided an electric discharge machinefor machining a workpiece in a desirable manner by applying electricdischarge machining voltage between an electrode and the workpiece whilefeeding the electrode and the workpiece relative to each other tocontrol a machining gap, which includes a spindle provided withattachment means for detachably attaching an electrode holder to thespindle, the electrode holder having an engagement portion for engagingwith the attachment means of the spindle and provided with electrodeholding means for holding the electrode in the electrode holder, anelectrode guide holder including an engagement portion for engaging withthe electrode holder and having attached thereto an electrode guide forsupporting and guiding the electrode, and electrode guide holdersupporting means for supporting the electrode guide holder so that theelectrode guide supports a distal end of the electrode, said electrodeguide holder supporting means having gripping means for gripping theelectrode guide holder and provided with moving means for moving theelectrode guide holder in parallel to an axis of the spindle.

In the machine according to the present invention, as described above,the electrode is held in advance, in the electrode holder on which theelectrode guide holder is then mounted, so that the electrode isinserted into the inner hole of the electrode guide attached to theelectrode guide holder, and after the electrode holder is mounted on thespindle, the electrode guide holder is moved to the distal end of theelectrode by the electrode guide holder supporting means so that theelectric discharge machining is carried out while the distal end of theelectrode being supported by the electrode guide. The spindle and atable are adapted to be movable relative to each other. Such aconstruction can eliminate a troublesome process of inserting theelectrode into the inner hole of the electrode guide every time theelectrode is exhausted due to the electric discharge machining and theelectrode holder is replaced, whereby it is possible to assuredly andextremely easily carry out the replacement of the electrode holder in ashort time. The electrode holder having the electrode attached theretomay be manually mounted on the spindle or may be mounted on the spindleby electrode holder replacement means.

According to a second aspect of the present invention, there is providedan electric discharge machine for machining a workpiece in a desirablemanner by applying electric discharge machining voltage between anelectrode and the workpiece while feeding the electrode and theworkpiece relative to each other to control a machining gap, whichincludes a spindle provided with attachment means for detachablyattaching the electrode or an electrode holder to the spindle, theelectrode holder having an engagement portion for engaging with theattachment means of the spindle and provided with electrode holdingmeans for holding the electrode in the electrode holder, an electrodeguide for supporting and guiding the electrode held in the electrodeholder, an electrode guide holder adapted to be detachably attached tothe electrode holder and having the electrode guide attached thereto,and electrode guide supporting means for supporting the electrode guide,the electrode guide supporting means having gripping means for grippingthe electrode guide or the electrode guide holder and provided withmoving means for moving the electrode guide or the electrode guideholder in parallel to an axis of the spindle.

In the machine according to the present invention, as described above,the electrode is held in advance in the electrode holder on which theelectrode guide is then mounted so that the electrode is inserted intothe inner hole of the electrode guide attached to the electrode holderand, after the electrode holder is mounted on the spindle, the electrodeguide is moved to the distal end of the electrode by the electrode guidesupporting means so that the electric discharge machining is carried outwhile the distal end of the electrode being supported by the electrodeguide. The electrode guide is directly mounted on the clamping meansprovided at the distal end of the electrode holder, and the electrodeguide supporting means is adapted to grip and move the electrode guideso that the electrode guide supports the distal end of the electrode.Either the spindle or the table may move as long as the spindle and thetable are adapted to be movable relative to each other. Such aconstruction can eliminate a troublesome process of inserting theelectrode into the inner hole of the electrode guide every time theelectrode is exhausted due to the electric discharge machining and theelectrode holder is replaced, whereby it is possible to assuredly andextremely easily carry out the replacement of the electrode holder in ashort time. Also, the electrode guide may be attached to the electrodeguide holder, which may be then detachably mounted on the electrodeguide. In such a case, the electrode guide supporting means grips theelectrode guide holder and moves it parallel to the axis of the spindleso that the electrode guide is moved to the distal end of the electrodeto support it.

Also, there is provided an electric discharge machine in which thespindle is attached to a spindle head, so that the spindle can be movedin a direction along the axis of the spindle and rotated about the axisof the spindle as well as be positioned at a desired position. Asdescribed above, the spindle is adapted to be movable in the directionof the axis thereof and rotatable about the axis thereof as well ascapable of being position controlled. Such a construction, in which atable having a heavy workpiece carried thereon is not movable while thespindle having the electrode attached thereto is movable, can make themoving part lighter in weight to stabilize the control operation of theelectric discharge machining.

Further, there is provided an electric discharge machine in which theelectrode holder has a flow path formed therein for introducing workingfluid into a pipe electrode when the pipe electrode is held therein.When the working fluid is supplied to the flow path, the working fluidis introduced into the pipe electrode and ejected from the distal end ofthe pipe electrode onto the part to be machined by the electricdischarge machining, whereby chips can be removed therefrom and themachining efficiency and accuracy can be improved.

Also, there is provided an electric discharge machine, in which theelectrode guide holder supporting means is attached to a suitableposition on the spindle head or a machine body and has gripping meansfor gripping the electrode guide holder, so that the electrode guideholder can be gripped by the gripping means to move parallel to the axisof the spindle and positioned at a desired position. As described above,the electrode guide holder supporting means is adapted to grip theelectrode guide holder and move it parallel to the axis of the spindle,so that the electric discharge machining is carried out, while thedistal end of the electrode being supported by the electrode guide, andthe position of the electrode guide can be adjusted in accordance withthe length of the electrode. Such a construction makes it possible toeasily and assuredly carry out the operation of replacing the electrodeholder. Further, as the position of the electrode guide is adjustable inaccordance with the length of the electrode, it is possible to guide andsupport the electrode always in a stable manner when the electrode isexhausted.

Also, there is provided an electric discharge machine, which furtherincludes electrode holder replacement means for transferring theelectrode holder between the spindle and an electrode magazine forstoring one or more electrode holders. As described above, a pluralityof electrode holders, each having the electrode held therein in advanceon which the electrode guide or the electrode guide holder is thenmounted, are stored in the electrode magazine so that the replacement ofthe electrode holder between the spindle and the electrode magazine canbe automatically carried out by the electrode holder replacement means.Such a construction eliminates a troublesome process of inserting theelectrode into the inner hole of the electrode guide every time when theelectrode holder is automatically replaced by the electrode holderreplacement means, whereby it is possible to assuredly carry out theautomatic replacement of the electrode holder and to carry out theelectric discharge machining including multiple processes for a longperiod in an unattended manner.

Also, there is provided an electric discharge machine in which theelectrode guide holder has a taper-shaped distal end opposed to theworkpiece, on which the electrode guide is detachably mounted. Asdescribed above, the distal end of the electrode guide holder is formedin a taper shape such as an inverse conical shape, and the electrodeguide is detachably mounted on the distal end by means of collet orothers so as to be easily detached from the distal end. Such aconstruction reduces a possibility of the interference between a devicefor guiding and supporting the electrode and the workpiece to facilitatethe access to the workpiece. The electrode guide can be replaced with anelectrode guide having a suitable hole diameter, depending on a diameterof the used electrode. If the inner hole of the electrode guide is worndue to the long-term use, the electrode guide is replaced with a freshone.

Also, there is provided an electric discharge machine which furtherincludes an anti-vibration guide movable toward and away from alengthwise middle portion of the electrode mounted on the spindle andcapable of holding and guiding the electrode when moving toward themiddle portion. In the case that the electrode holder holds a thin andlong electrode, the anti-vibration guide can hold and guide the middleportion of the length of the electrode to prevent the electrode fromvibrating or bending.

To achieve the above-mentioned object, according to a third aspect ofthe present invention, there is further provided a method for machininga workpiece in a desirable manner by applying electric dischargemachining voltage between an electrode and the workpiece while feedingthe electrode and the workpiece relative to each other to control amachining gap, which includes the steps of: (a) mounting an electrodeguide or an electrode guide holder on an electrode holder having anelectrode held therein in advance; (b) mounting the electrode holder ona-spindle manually or by electrode holder replacement means; (c) movingthe electrode guide to a distal end or the electrode to support theelectrode; and (d) moving the electrode and the workpiece relative toeach other to position the electrode at a position of the workpiece tobe machined and start the electric discharge machining.

As described above, according to this method, the electrode is held inthe electrode holder in advance, on which the electrode guide or theelectrode guide holder is then mounted, and after the electrode holderis mounted on the spindle, the electrode holder or the electrode guideholder is gripped by electrode guide supporting means or electrode guideholder supporting means and moved downward so that the electrode guidemoves to the distal end of the electrode and supports the electrode,after which the electrode is positioned at a position of the workpieceto be machined by moving the electrode and the workpiece relative toeach other and the electric discharge machining is started. Such aconstruction can eliminate a troublesome process of inserting theelectrode into the inner hole of the electrode guide every time when theelectrode is exhausted due to the electric discharge machining and theelectrode holder is replaced, whereby it is possible to assuredly andeasily carry out the replacement of the electrode holder and the workingefficiency of the electric discharge machining is improved.Particularly, in the case that the fine hole is machined, it was a verydifficult and time-consuming operation to automatically insert a thinelectrode into the inner hole of the electrode guide. The methodaccording to the present invention makes it possible to easily carry outsuch a operation to solve a problem.

According to a fourth aspect of the present invention, there is provideda method for machining a workpiece in a desirable manner by applyingelectric discharge machining voltage between an electrode and theworkpiece while feeding the electrode and the workpiece relative to eachother to control a machining gap, which includes the steps of: mountingon a spindle of an electric discharge machine the electrode or anelectrode holder having the electrode held therein; inserting theelectrode into an electrode guide or an electrode guide holder grippedby electrode guide supporting means for supporting the electrode guidemovable parallel to an axis of the spindle so that a distal end of theelectrode is supported by the electrode guide; moving the electrode andthe workpiece relative to each other to position the electrode at aposition on the workpiece to be machined; and applying electricdischarge machining voltage between the electrode and the workpiecewhile feeding the electrode and the workpiece relative to each other tocarry out the electric discharge machining on the workpiece.

After the electrode or the electrode holder having the electrode heldtherein is mounted on the spindle, the spindle or the electrode guidesupporting means is moved parallel to the axis of the spindle, therebyto insert the electrode into the electrode guide gripped by theelectrode guide supporting means positioned at a position closer to thedistal end of the electrode. After the distal end of the electrode issupported in this way by the electrode guide, the electrode ispositioned at a position on the workpiece to be machined, and theelectric discharge machining of the workpiece is started by applying theelectric discharge machining voltage between the electrode and theworkpiece.

According to a fifth aspect of the present invention, there is provideda method for machining a workpiece in a desirable manner by applying anelectric discharge machining voltage between an electrode and theworkpiece while feeding the electrode and the workpiece relative to eachother to control a machining gap, which includes the steps of: holdingthe electrode in an electrode holder; mounting an electrode guide holderon the electrode holder so that the electrode is inserted into anelectrode guide of the electrode guide holder; accommodating theelectrode holder in an electrode magazine of an electric dischargemachine; taking out the electrode holder from the electrode magazine byelectrode holder replacement means and mounting the electrode holder ona spindle of the electric discharge machine; releasing the mounting ofthe electrode guide holder on the electrode holder and moving theelectrode guide holder parallel to an axis of the spindle so that adistal end of the electrode is supported by the electrode guide; movingthe electrode and the workpiece relative to each other to position theelectrode at a position on the workpiece to be machined; and applying anelectric discharge machining voltage between the electrode and theworkpiece while feeding the electrode and the workpiece relative to eachother to carry out the electric discharge machining on the workpiece.

The electrode is held in the electrode holder and the electrode guideholder is mounted on the electrode holder so that the electrode isinserted into the electrode guide of the electrode guide holder. Theelectrode holders in this state are accommodated in the electrodemagazine, and one of them is taken out from the electrode magazine bythe electrode holder replacement means and mounted on the spindle.Thereafter, the electrode guide holder is gripped by moving theelectrode guide holder supporting means parallel to the axis of thespindle. The mounting of the electrode guide holder on the electrodeholder is released, and the electrode guide holder is moved by theelectrode guide holder supporting means to the distal end of theelectrode and stopped there. This enables the electrode guide to supportthe distal end of the electrode, and after the electrode is positionedat a position on the workpiece to be machined, the electric dischargemachining is started.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be described in more detail below based on the preferredembodiments of the present invention with reference to the accompanyingdrawings, wherein:

FIG. 1 is a side view illustrating an electric discharge machineaccording to an embodiment of the present invention;

FIG. 2 is a sectional view of a first embodiment of the presentinvention illustrating an electrode holder on which an electrode guideholder is mounted;

FIG. 3 is a top view of FIG. 2;

FIG, 4 is a sectional view taken along a line IV-IV in FIG. 2;

FIGS. 5A to 5E are views for illustrating the operations during thereplacement of the electrode holder according to the present invention;

FIG. 6 is a sectional view of a second embodiment of the presentinvention illustrating an electrode holder on which an electrode guideholder is mounted; and

FIG. 7 is a sectional view taken along a line VII-VII in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

In FIG. 1, a workpiece 3 is mounted on a table 1 provided on a base ofan electric discharge machine not shown, and a work tank 5 for storingworking fluid therein is provided so as to encircle the table 1 and theworkpiece 3. A column 7 is provided on the base so as to be movable in adirection shown by an arrow X, and a ram 9 is provided on the column 7so as to be movable in a direction shown by an arrow Y. A spindle head11 is mounted on a front surface of the ram 9, and a spindle 13 isprovided in the spindle head 11. The spindle 13 can be moved in adirection shown by an arrow Z, i.e. a direction parallel to an axis ofthe spindle 13, by a controller (not shown) activating a servo motor 15,and be positioned at any position. Also, the spindle 13 can be rotatedabout the axis of the spindle 13 as shown by an arrow C by the drive ofa servo motor 17 and be positioned at any angular position. A knownattachment means 19, such as a chuck commonly employed for detachablymounting an electrode holder 23 onto a distal end of the spindle 13, isprovided.

A rod-like or a pipe-like electrode 21 used for machining a fine hole inthe workpiece 3 is attached in advance to the electrode holder 23, whichis then mounted on the spindle 13 with an electrode guide holder 25mounted thereon. The electrode holder 23 with the electrode guide holder25 mounted thereon is placed in an electrode magazine 27. An electrodeguide holder supporting means 29 for supporting the electrode guideholder is attached to the column 7 via a bracket 31 and is adapted to bemovable in a direction shown by an arrow W and to be capable of beingpositioned at any position. Further, the electrode guide holdersupporting means 29 is rotatable as shown by an arrow R and is adaptedto carry the electrode holder 23. The electrode guide holder supportingmeans 29 is provided at a distal end thereof with a gripper 35 forgripping the electrode holder 23 and/or the electrode guide holder 25,which is adapted to be driven by a drive device 37 to move in adirection shown by an arrow S when it is desired to grip or release theelectrode guide holder 25. The gripper 35 is of a gripping claw typesimilar to those commonly employed in a tool exchanger for a machiningcenter or others.

The electrode guide holder supporting means 29 grips the electrodeholder 23 by the gripper 35 and transfers it to the spindle side by therotation shown by the arrow R to mount the electrode holder 23 on thespindle 13. On the contrary, the electrode guide holder supporting means29 grips the electrode holder 23 mounted on the spindle 13 by thegripper 35 and transfers it to the electrode magazine side by therotation shown by the arrow R to place the electrode holder 23 in theelectrode magazine 27. FIG. 1 is a view showing a state in which theelectrode guide holder supporting means 29 grips the electrode guideholder 25 and moves it to a distal end of the electrode 21. In analternative embodiment, electrode holder replacement means may beprovided for exchanging the electrode holder 23 between the electrodemagazine 27 and the spindle 13. This electrode holder replacement meansis a device similar to the commonly employed known ones and, therefore,the explanation thereof will be omitted. FIG. 5A schematicallyillustrates an operation of an electrode holder replacement arm 91 ofthe electrode holder replacement means.

A system for exchanging the electrode holder 23 between the spindle 13and the electrode magazine 23 may be a so-called armless exchangersystem wherein the electrode holder 23 is directly transferred betweenthe spindle 13 and the electrode magazine 23. In FIG. 1, after an emptymounting pocket of the electrode magazine 27 is indexed forward and theelectrode magazine 27 is advanced as a whole in the Y-direction, theelectrode holder 23 is held in the empty mounting pocket. After thespindle 13 is once retreated upward and another electrode holder 23 tobe newly mounted on the spindle 13 is indexed in the electrode magazine27, the spindle 13 is descended and the new electrode holder 23 ismounted on the spindle 13. Then, the electrode magazine 27 is retreatedin the Y-direction, thereby to complete the automatic replacement of theelectrode holder 23.

In FIGS. 2, 3 and 4, the electrode holder 23 includes an electrodeholding section 51 for holding the electrode 21, four projections 53 forlocking the electrode guide holder 25, a groove 55 for the electrodeholder replacement arm 91 to grip the electrode holder 23, and a pullstud 57 for mounting the electrode holder 23 on the spindle 13. The pullstud 57, an outer circumference 57 a of a mount seat of the pull stud57, and a top surface 23 a of the electrode holder 23 constitute anengagement portion with attachment means not shown. The pull stud 57 ispulled into the interior of the spindle 13 by a collet provided at adistal end of a draw bar biased with a spring force of a disc spring,thereby to mount the electrode holder 23 on the spindle 13. When thedraw bar is moved forward against the spring force of the disc spring byan unclamp cylinder (not shown) provided behind the draw bar, the pullstud 57 is released to detach the electrode holder 23 from the spindle13. The electrode 21 is detachably held in the electrode holding section51 by means of a spring collet 41 and a nut 43 commonly employed in theart. A flow path 59 is formed through a center portion of the electrodeholder 23 to allow a working fluid to pass therethrough when thepipe-like electrode is used for the machining.

The electrode guide holder 25 includes an electrode guide 61 removablyfastened to a slotted portion 45 by a screw 47, projections 65 forengaging with the projections 53 of the electrode holder 23, recesses 67formed between the projections, and a Curvic coupling 49 for positioningthe electrode guide holder 25 with regard to a gripper section 39 of theelectrode guide holder supporting means 29. A lower tip end of theelectrode guide holder 25 is tapered, for example, to have an inverseconical shape for the purpose of avoiding interference with theworkpiece 3. In FIG. 2, while slotting is used as means for fixing theelectrode guide 61 at a distal end of the electrode guide holder 25, acollet or a known clamping means commonly employed in the prior art maybe alternatively used for detachably mounting the electrode guide 61 onthe distal end of the electrode guide holder 25. The electrode guide 61is preferably made of hard and durable material such as sapphire orceramic. In this regard, the electrode guide holder 25 may be integralwith the electrode guide 61.

A pushing piece 71 and a spring 73 are provided in the electrode guideholder 25 for pushing the electrode holder 23 upward. As shown in FIGS.2 and 4, there are three radially extending grooves 87 formed in thepushing piece 71, in which three pins 89 fixed to the electrode holder23 are fitted respectively. Specifically, when the electrode holder 23pushes the pushing piece 71 downward and is then rotated in thedirection as shown by the arrow C, the pushing piece 71 is rotated alongwith the electrode holder 23. Further, three pins 97 are provided on theouter circumference of the pushing piece 71 to protrude radially throughwindows 99 formed in the electrode guide holder 25.

On the other hand, the gripper section 39 of the electrode guide holdersupporting means 29 is of a ring shape which is different from thegripping claw type gripper 35 shown in FIG. 1. The gripper section 39 isformed with an annular projecting portion 101, which is notched by threegrooves 103 at three sites in the circumferential direction. In a statewherein the electrode holder 23 having the electrode guide holder 25mounted thereon is mounted on the spindle 13, when the electrode guideholder supporting means 29 moves upward in the direction shown by thearrow W, the Curvic couplings 49 are intermeshed with each other becausethe pins 97 are aligned with the grooves 103, and then, the upwardmotion of the electrode guide holder supporting means 29 is made tostop. Thereafter, the spindle 13 is lowered by a predetermined smalldistance in the Z-axis direction to push down the pushing piece 71, andthen rotated by 45 degrees in a direction opposite the direction shownby the arrow D to rotate the electrode holder 23 along with the spindle13. Next, when the spindle 13 is moved up by the above-mentionedpredetermined small distance, the pins 97 are engaged with theprojecting portion 101 by a pressing force of the spring 73, so that theelectrode holder 25 is gripped by the gripper section 39. Simultaneouslytherewith, the electrode holder 23 is released from the electrode guideholder 25. The procedure for attachment/detachment of the electrodeholder 23 and the electrode guide holder 25 will be described later.

The electrode 21 is manually held in advance in the electrode holdingsection 51 of the electrode holder 23, on which the electrode guideholder 25 is then mounted. Thereafter, a plurality of electrode holders23, each having the electrode guide holder 25 mounted thereon, areplaced in the electrode magazine 27. Thus, the preparation is completed.When the electrode guide holder 25 is mounted on the electrode holder23, the projections 53 of the electrode holder 23 are aligned with therecesses 67 of the electrode guide holder 25, and inserted thereinto bylowering the pushing piece 71, after which the electrode holder 23 isrotated by 45 degrees in the direction shown by the arrow D whereby theprojections 53 are engaged with the projections 65 by the pressing forceof the spring 73 to mount the electrode guide holder 25 on the electrodeholder 23. When the electrode guide holder 25 is detached from theelectrode holder 23, the electrode holder 23 is slightly pushed down androtated by 45 degrees in the direction opposite to the direction shownby the arrow D to disengage the projections 53 from the projections 65,after which the electrode guide holder 25 is moved down and removed fromthe electrode holder 23.

FIGS. 5A to 5E are views for illustrating the operations carried out forautomatically replacing the electrode holder 23 by using electrodeholder replacement means and starting the electric discharge machining.In FIG. 5A, the spindle 13 is movable in the direction shown by thearrow Z and rotatable in the direction shown by the arrow C with regardto the spindle head 11 provided above the table 1. The attachment means19 for attaching or detaching the electrode holder 23 to or from thespindle 13 is provided at a distal end of the spindle 13. A gripper arm29 having the gripper section 39 used as the electrode guide holdersupporting means is attached to the spindle head 11 via the bracket 31.The gripper arm 29 can be moved and positioned in the direction shown bythe arrow W by a drive device not shown, and the gripper section 39 ispositioned beneath the electrode 21. The electrode holder replacementarm 91 in the electrode holder replacement means grips the electrodeholder 23 having the electrode 21 and the electrode guide holder 25mounted thereon, to pick it up from the electrode magazine 27 andposition the electrode holder 23 beneath the spindle 13 by the movementof the arm 91 in the direction shown by an arrow H.

FIG. 5B illustrates a state wherein the spindle 13 is descended in thedirection shown by the arrow Z, the attachment means 19 of the spindle13 clamps the electrode holder 23, and the electrode holder replacementarm 91 is retreated to a retreated position. FIG. 5C illustrates a statewherein the gripper arm 29 is moved up in the direction shown by thearrow W and the gripper section 39 is intermeshed with the electrodeguide holder 25 via the Curvic couplings 49. FIG. 5D illustrates a statewherein the spindle 13 is rotated by 45 degrees as shown by the arrow Cso that the gripper section 39 grips the electrode guide holder 25 andthe electrode holder 23 is disengaged from the electrode guide holder25, after which the gripper arm 29 is descended in the direction shownby the arrow W while the gripper section 39 grips the electrode guideholder 25, thereby to move the electrode guide 61 to the distal end ofthe electrode 21.

FIG. 5E illustrates a state wherein the gripper arm 29 is descended inthe direction shown by the arrow W in synchronism with the downwardmovement of the spindle 13 in the direction shown by the arrow Z and theelectrode 21 is positioned to a machining position on the workpiece 3 tobe machined. In this regard, the positioning of the electrode 21relative to the workpiece 3 may, of course, be achieved by moving up thetable 1 relative to the spindle which is stationary. When the fine holeis machined, the electrode 21 must be thin and long. Therefore,vibration and/or bending of the electrode may occur. To prevent suchvibration and/or bending, a known anti-vibration guide 93 commonlyemployed in the prior art is attached to the spindle head 11 via abracket 95. The anti-vibration guide 93 is movable forward and rearwardby a drive device not shown. The anti-vibration guide 93 is notindispensable but desirable.

Next, an electrode guide holder 25 according to a second embodiment ofthe present invention will be described with reference to FIGS. 6 and 7.In FIGS. 6 and 7, the same elements as in the first embodiment aredenoted by the same reference numerals.

An electrode guide 61 is detachably fastened to the electrode guideholder 25 by a set screw 63. The electrode guide 61 may be integral withthe electrode guide holder 25. In such a case, the electrode guideholder 25 and the electrode guide 61 could be regarded as a singleelectrode guide as a whole. While an electrode fixing section 51 of anelectrode holder 23 is not shown in detail in the drawings, it may beconstituted by a spring collet and a nut as in the embodiment shown inFIG. 2 or may have a construction different therefrom.

In order to engage the electrode guide holder 25 with the electrodeholder 23, projections 53 of the electrode holder 23 are aligned withrecesses 67 of the electrode guide holder 25 to insert the electrodeholder 23 into the electrode guide holder 25, a pushing piece 71 ispushed down against a pressing force of a spring 73 and then rotated by45 degrees in the direction shown by the arrow D, and the pushing downof the pushing piece is stopped. Due to these steps, the pushing piece71 is pushed up by the pressing force of the spring 73 to bring theprojections 53 into contact with the projections 65 and engage theelectrode guide holder 25 with the electrode holder 23. Steps reversethereto disengage the electrode guide holder 25 from the electrodeholder 23.

The positioning of the gripper section 39 of the electrode guide holdersupporting means 29 relative to the electrode guide holder 25 is carriedout by inserting the electrode guide holder 25 into an inner hole 77 ofthe gripper section 39 to fit projections 79 of the gripper section 39in four grooves 69 of the electrode guide holder 25. At the same time, aplurality of balls 81 biased by elastic members 83 and set screws 85move into grooves 75 formed in the electrode guide holder 25, thereby togrip the electrode guide holder 25 in the electrode guide holdersupporting means 29. If the electrode holder 23 and the electrode guideholder 25 according to the second embodiment are used, the steps for thereplacement of the electrode holder shown in FIGS. 5A to 5E are the sameas in the first embodiment.

Although not shown, in one arrangement, a clamp means such as a colletor the like may be provided at a distal end of the electrode holdingsection 51 so that the electrode guide 61 for inserting the electrode 21thereinto can be detachably mounted on the clamp means. Electrode guidesupporting means having a gripper section for gripping the electrodeguide 61 may be adapted to directly grip the electrode guide 61 by thegripper section to move it parallel to an axis of the spindle 13 so thatthe electric discharge machining can be carried out while a distal endof the electrode 21 is supported by the electrode guide 61.

In the case that the electrode guide holder 25 shown in FIG. 6 is used,a gripper member of the electrode guide holder supporting means 29 cangrip the electrode guide holder 25 mounted on the electrode holder 23clamped in the electrode magazine 27, and laterally pulls the electrodeguide holder 25 out of the electrode magazine 27 for the purpose oftransfer. Also, as shown in FIG. 5A, if an electrode holder replacementarm 91 used only for replacing the electrode is provided separately fromthe electrode guide holder supporting means 29, it is possible tosmoothly carry out the electrode replacement even if a distance betweenthe electrode magazine 27 and the spindle 13 is long and/or theelectrode holder 23 is heavy.

While this embodiment has been described based on the case in whichrod-like or pipe-like electrode is used for machining a fine hole, thesame apparatus and method are also applicable to a thin-plate-type oflong electrode. Further, while the electrode 21 is mounted on thespindle 13 by using the electrode holder 23 in this embodiment, it isalso possible to directly mount the electrode on the spindle by theattachment means 19 of the spindle 13. In such a case, the attachmentmeans 19 includes a chuck structure capable of gripping either of theelectrode and the electrode holder. Irrespective of using the electrodeholder or not, after mounting the electrode on the spindle, theelectrode guide or the electrode guide holder and the electrode may bemoved relative to each other in the direction shown by the arrow Z toinsert the electrode into the electrode guide and support a distal endof the electrode by the electrode guide supporting means or theelectrode guide holder supporting means. Thereby, when a plurality ofelectrodes of the same diameter are used for machining fine holes, thereis no need for preparing the same number of electrode guide holders asthat of the electrodes, which is economical.

As described hereinbefore, according to the present invention, theelectrode is held in advance in the electrode holder, on which theelectrode guide holder is mounted, with the electric guide inserted intothe electric holder. After the electric holder is then mounted on thespindle, the electrode guide or the electrode guide holder is moved tothe distal end of the electrode so that the distal end of the electrodeis supported by the electrode guide. Therefore, a troublesome process ofinserting the electrode into the inner hole of the electrode guide everytime when the electrode holder is replaced can be eliminated, whichmakes it possible to assuredly carry out the replacement of theelectrode holder and results in the improved machining efficiency. Also,as the electrode holder replacement means is further added, it ispossible to assuredly carry out the automatic replacement of theelectrode holder to realize automatic multi-process electric dischargemachining for a long period. Further, since the distal end of theelectrode guide holder is formed in an inverse conical shape and theelectrode guide is attached thereto, the possibility of interference ofthe workpiece with the apparatus is reduced, thereby to improve theaccessibility to the workpiece.

As the electrode guide supporting means and the electrode guide holdersupporting means can be positioned at any position, it is possible toadjust the position of the electrode guide depending on a length of theelectrode when the electrode is exhausted and becomes shorter, so thatthe electrode is always guided and supported in a stable state. Aworking fluid introduced into a center hole of the pipe-like electrodethrough a flow path formed in the electrode holder is ejected from thedistal end of the pipe-like electrode, which facilitates the dischargeof chip generated during the machining of the fine hole to improve themachining accuracy and the machining efficiency. Further, as theelectrode guide is detachably mounted on the electrode guide holder, itis possible to easily replace the electrode guide in a short time.Provision of the anti-vibration guide makes it possible to hold andguide a middle portion of the thin and long electrode, thereby to avoidthe vibration or bending of the electrode and achieve a high precisionmachining of a fine hole or a thin slit. The above-mentioned methodmakes it possible to eliminate a troublesome process of inserting theelectrode into the inner hole of the electrode guide every time when theelectrode holder is replaced, thereby to assuredly carry out theoperation for the replacement of the electrode and improve the operatingefficiency of the electric discharge machining.

1. An electric discharge machine having an electrode for machining aworkpiece by applying electric discharge machining voltage between saidelectrode and said workpiece while feeding said electrode and saidworkpiece relative to each other to control a machining gap, saidelectric discharge machine comprising: a spindle and an electrode holderfor carrying said electrode, said spindle being provided with attachmentmeans for detachably attaching said electrode holder to said spindle;said electrode holder having an engagement portion for engaging withsaid attachment means of said spindle, wherein said electrode holder isprovided with an electrode holding means for holding said electrode insaid electrode holder; an electrode guide holder including an engagementportion for detachably engaging with said electrode holder, saidelectrode guide holder having attached thereto an electrode guide forsupporting and guiding said electrode; and electrode guide holdersupporting means for supporting said electrode guide holder for causingsaid electrode guide holder to selectively disengage from said electrodeholder and for moving said electrode guide holder along said electrodeto the distal thereof so that said electrode guide attached to saidelectrode guide holder supports said distal end of said electrode, saidelectrode guide holder supporting means having gripping means forgripping said electrode guide holder and being provided with movingmeans for moving said electrode guide holder.
 2. The electric dischargemachine according to claim 1, wherein said electrode guide holdersupporting means is attached to a suitable position on said spindle heador a machine body and has gripping means for gripping said electrodeguide holder, so that the electrode guide holder can be gripped by saidgripping means to move parallel to the axis of said spindle andpositioned at a desired position.
 3. An electric discharge machineincluding an electrode for machining a workpiece by applying electricdischarge machining voltage between a said electrode and said workpiecewhile feeding said electrode and said workpiece relative to each otherto control a machining gap, said electric discharge machine comprising:a spindle and an electrode holder, said spindle being provided withattachment means for detachably attaching said electrode or saidelectrode holder to said spindle; said electrode holder having anengagement portion for engaging with said spindle attachment means andbeing provided with electrode gripping means for fixing the position ofsaid electrode in said electrode holder; an electrode guide forsupporting and guiding said electrode held in said electrode holder; anelectrode guide holder adapted to be detachably attached to saidelectrode holder and having said electrode guide attached thereto, saidelectrode guide remaining supporting and guiding said electrode aftersaid detachment from electrode holder; and electrode guide supportingmeans for supporting said electrode guide, said electrode guidesupporting means having gripping means for gripping said electrode guideor said electrode guide holder and provided with moving means for movingsaid electrode guide or said electrode guide holder in parallel to anaxis of said spindle.
 4. The electric discharge machine according toclaim 1 or 3, wherein said spindle is attached to a spindle head, sothat said spindle can be moved in a direction along the axis of saidspindle and rotated about the axis of said spindle as well as bepositioned at a desired position.
 5. The electric discharge machineaccording to claim 1 or 3, wherein said electrode holder has a flow pathformed therein for introducing working fluid into a pipe electrode whensaid pipe electrode is held therein.
 6. The electric discharge machineaccording to claim 1 or 3, further comprising electrode holderreplacement means for transferring said electrode holder between saidspindle and an electrode magazine for storing one or more electrodeholders.
 7. The electric discharge machine according to claim 1 or 3,wherein said electrode guide holder has a tapered-shaped distal endopposed to said workpiece, on which said electrode guide is detachablymounted.
 8. The electric discharge machine according to claim 1 or 3,further comprising an anti-vibration guide movable toward and away froma lengthwise middle portion of said electrode mounted on said spindleand capable of holding and guiding said electrode.
 9. A method formachining a workpiece in a electric discharge machine by applyingelectric discharge machining voltage between an electrode and saidworkpiece while feeding said electrode and said workpiece relative toeach other to control a machining gap, said electric discharge machinecomprising a spindle provided with attachment means for detachablyattaching an electrode holder to said spindle, said electrode holderhaving an engagement portion for engaging with said attachment means ofsaid spindle and provided with electrode holding means for holding saidelectrode in said electrode holder, an electrode guide holder includingan engagement portion for engaging with said electrode holder and havingattached thereto an electrode guide for supporting and guiding saidelectrode, and electrode guide holder supporting means for supportingsaid electrode guide holder so that said electrode guide supports adistal end of said electrode, said electrode guide holder supportingmeans having gripping means for gripping said electrode guide holder andprovided with moving means for moving said electrode guide holder inparallel to an axis of said spindle, said method comprising the stepsof: (a) mounting said electrode guide holder on said electrode holderhaving an electrode held therein in advance; (b) mounting said electrodeholder with said mounted electrode guide holder onto said spindlemanually or by electrode holder replacement means; (c) gripping saidelectrode guide holder by said electrode guide holder supporting meansand moving said electrode guide holder apart from said spindle mountedelectrode holder to said distal end of said electrode to support saidelectrode with said electrode guide; and (d) moving said electrode andsaid workpiece relative to each other to position said electrode at aposition on said workpiece to be machined and start the electricdischarge machining.
 10. A method for machining a workpiece in anelectric discharge machine by applying electric discharge machiningvoltage between an electrode and said workpiece, said electric dischargemachine having a spindle provided with attachment means, an electrodeholder provided with electrode holding means for holding said electrode,an electrode guide holder for engaging with said electrode holder andhaving an electrode guide for supporting and guiding said electrode, andelectrode guide holder supporting means for supporting said electrodeguide holder and having gripping means for gripping said electrode guideholder, said method comprising the steps of; mounting on said spindlesaid electrode or said electrode holder having said electrode heldtherein and said electrode guide holder mounted thereabout; positioningsaid electrode guide holder at the distal end of said electrode byinserting said electrode into said electrode guide or by gripping saidelectrode guide holder by said electrode guide supporting means andmoving it so that a distal end of said electrode is supported by saidelectrode guide; moving said electrode and said workpiece relative toeach other to position said electrode at a position on said workpiece tobe machined; and applying electric discharge machining voltage betweensaid electrode and said workpiece while feeding said electrode and saidworkpiece relative to each other to carry out the electric dischargemachining on said workpiece.
 11. A method for machining a workpiece inan electric discharge machine, said electric discharge machine having anelectrode, a spindle provided with an attachment member an electrodeholder having an engagement portion, an electrode guide holder having anengagement portion and an electrode guide for supporting and guidingsaid electrode, electrode guide holder supporting means for supportingsaid electrode guide holder and having gripping means for gripping saidelectrode guide holder, being also provided with moving means for movingsaid electrode guide holder, and electrode holder replacement means fortransferring said electrode holder with an electrode held therebybetween said spindle and an electrode magazine, said method comprisingthe steps of: holding said electrode in said electrode holder; mountingsaid electrode guide holder on said electrode holder so that saidelectrode is inserted into said electrode guide of said electrode guideholder; accommodating said electrode holder in said electrode magazine;taking out said electrode holder from said electrode magazine by saidelectrode holder replacement means and mounting said electrode holderwith said electrode and said electrode guide holder onto said spindle;releasing the mounting of said electrode guide holder on said electrodeholder and moving said electrode guide holder parallel to an axis ofsaid spindle by said electrode guide holder supporting means so thatsaid distal end of said electrode is supported by said electrode guide;moving said electrode and said workpiece relative to each other toposition said electrode at a position on said workpiece to be machined;and applying electric discharge machining voltage between said electrodeand said workpiece while feeding said electrode and said workpiecerelative to each other to carry out the electric discharge machining onsaid workpiece.